1. NEC LABORATORIES EUROPE, NEC EUROPE LTD., RATHAUSALLEE 10, D-53757 SANKT AUGUSTIN, GERMANY,
2. NEC LABORATORIES EUROPE, NEC EUROPE LTD., RATHAUSALLEE 10, D-53757 SANKT AUGUSTIN, GERMANY
3. MATHEMATICS AND COMPUTER SCIENCE DIVISION, ARGONNE NATIONAL LABORATORY, ARGONNE, IL 60439, USA
4. DEPARTMENT OF COMPUTER SCIENCE, UNIVERSITY OF ILLINOIS, URBANA, IL 61801, USA